“Through an analysis of chimpanzee-human discourse, we show
that two Pan troglodytes [the usual] chimpanzees and two
Pan paniscus [pigmy] chimpanzees (bonobos) exposed to a
humanly devised symbol system use partial or complete repetition
of others’ symbols, as children do: they do not produce rote imitations,
but instead use repetition to fulfil a variety of pragmatic functions
in discourse. These functions include agreement, request, promise,
excitement, and selection from alternatives. In so doing the
chimpanzees demonstrate contingent turn-taking and the use of
simple devices for lexical cohesion. In short, they demonstrate
conversational competence. Because of the presence of this conversational
competence in three sibling species, chimpanzees, bonobos, and
humans, it is concluded that the potential to express pragmatic
functions through repetition was part of the evolutionary hisotry
of human language, present in our common ancestor before the phylogenetic
divergence of hominids and chimpanzees. In the context of these
similarities, two interesting differences appeared: (1) Human
children sometimes used repetition to stimulate more talk in their
conversational partner; the chimpanzees, in contrast, use repetition
exclusively to forward the non-verbal action. This difference
may illuminate a unique feature of human linguistic communication,
or it may simply reflect a modality difference (visual symbols
used by the chimpanzees, speech use by the children) in the symbol
systems considered in this research. A second difference seems
likely to reflect a true species difference: utterance length.
The one- and two-symbol repetitions use by the chimpanzees to
fulfil a variety of pragmatic functions were less than half the
maximum length found in either the visual symbol combinations
addressed to them by their adult human caregivers or the oral
repitions of two-year-old children. This species difference probably
reflects the evolution of increased brain size and consequent
increased memory capacity that has occurred since the phylogenetic
divergence of hominids and chimpanzees four to seven million years
ago.”

METHODS (p. 7)

They used a method of discourse analysis based on that published
by Ochs Keenan (1977) for children.

EXPLORATORY STUDY (p. 9)

Used Austin and Sherman when they were 7 and 8 yrs old, and had
100 lexigrams available to them. A computer printout of all symbol
use by the researcher and subject was analysed in relation to
detailed contextual notes made by the researcher. Two sessions
of about an hour with each animal were analysed. (Transcripts
had been published in 1984). 5 and 6 instances of “Confirm/agree”
and “Request” were recorded for Austin, and 9, 3 and
5 instances of “Confirm/agree”, “Confirm with specification”
and “Counterclaim” were observed for Sherman.

MAIN STUDY (p. 15)

Used Kanzi and Mulika when they were 5 and almost 2 years old.
The analysis was based on every lexigram they produced during
one month.

Mulika had 87 repetitions: 37 (43%) were “Confirm/agree”
and 46 (53%) were either “Request” or “Imitate/Request”.

Kanzi had 62 repetitions: 46 (74%) were “Confirm/agree”
and 10 (22%) were either “Request” or “Imitate/request”.

The authors claim that repetition of symbols cannot be used as
a dividing line between human and chimpanzee, since the reptitions
in chimpanzees are similar to some of the simplest occurring in
1- and 2-yr old children. However, they acknowledge that children’s
repitions become very different. “A principle difference
was that repetitions were used by children, but not chimpanzees,
to keep conversation going, to elicit further verbalization. .....
This difference .... could show that motivation to keep a conversation
going and to use language for its own sake is, among primates,
unique to the human species. Secondly, children develop symbolic
means of referring to pragmatic functions, and the chimpanzees
studied did not do this (e.g. did not have anything corresponding
to “I agree”). Thirdly, chimpanzee repetitions were
primarly of single lexigrams, whereas children often repeat several
words. The authors accept that sentence length is probably “a
true species difference” (p. 22).

Although these studies draw attention to the fact that symbol
repetition by chimps is not necessarily just blind imitation,
they also support the position that chimpanzee symbol use is unlike
human language in being a) syntactically very limited; and b)
tied very closely to immediate goals.

Thus the work by Greenfield and Savage-Rumbaugh, Jensvold and Gardner (2000) and Bodamer and Gardner (2002) does
little to alter the conclusion of an immense gap between trained
apes and human infants (e.g. Rivas, 2005): the 1990 chapter
has Kanzi doing ‘action precedes object’ only about twice a week
with 96% of his output judged to be requests, while Greenfield
and S-R (1993) admit that their subjects used repetitions only
for requests, not conversationally or to express agreement.

Similarly the results reported by Jensvold and Gardner (2000) and Bodamer and Gardner (2002) can readily be interpreted as Thorndikean conditioned responses reinforced by tangible goals, as opposed to human-like conversations.